Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions. Traditionally, the amount of EGR routed through the EGR system is measured and adjusted based on engine speed, engine temperature, and load during engine operation to maintain desirable combustion stability of the engine while providing emissions and fuel economy benefits. Such EGR systems can reduce engine knock, in-cylinder heat losses, throttling losses, as well as NOx emissions. However, providing a desired engine dilution assumes an even distribution of EGR gas across engine intake air to maintain desirable combustion stability. From this, the performance of the engine EGR is largely determined by the flow mixing between intake air and EGR flow. A traditional “Y” shaped design of EGR mixers may be utilized to separate and distribute EGR flow into the intake passage.
Other attempts to address EGR mixing include expelling EGR gas from an EGR outlet into a venturi throat in an intake passage. One example approach is shown by Vaught et al. in U.S. Pat. No. 8,056,340. Therein, an annular EGR outlet is fluidly coupled to an intake passage directly downstream of a venturi throat of a venturi passage. The venturi passage comprises a protrusion adjacent the venturi throat to create an intake air turbulence to increase EGR mixing.
However, the inventors herein have recognized potential issues with such designs. As one example, EGR may not adequately mix with intake flowing through the intake passage. Consequently, a discrepancy between the concentration of EGR and intake air may lead to stratified distribution and non-uniformed temperature distribution, compromising the air/fuel mixture flowing into the engine intake for combustion.
In one example, the issues described above may be addressed by a system for a surface, such as a rounded surface, upstream of an engine and downstream of an EGR outlet, the surface comprising a plurality of venturi tubes extending in an upstream direction, where the venturi tubes are configured to receive intake air and EGR upstream of the surface and expel intake air and EGR downstream of the surface. In this way, intake air and exhaust gas flow through the venturi tubes before flowing through the circular surface.
As one example, intake air and exhaust gas are forced to flow through the venturi tubes before flowing to the engine. The surface, which may be circular in one example, may be impervious to and blocks gas flow. The mixer may be hollow and allow intake air and exhaust gas to flow between the venturi tubes. As gas flows through the venturi tubes, a vacuum is generated in the venturi tubes at a constriction of the venturi passages. Openings are located at the constriction of the venturi passages and as a result, vacuum from the venturi passages is provided to spaces between the venturi tubes. As such, gas may flow into the venturi tubes via a venturi inlet of through the openings. Intake gas and exhaust gas may mix in the venturi tubes or in the spaces between the venturi tubes, before flowing through the circular surface via venturi outlets. The homogeneity of intake air and exhaust gas is increased, which may result in improved engine performance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.